Its not exactly a feature, but I don't think I have ever peeped through the small triangular quarter glass in my Punto!
Fog lamps are also something I very rarely use.
The backup fuel-cap release thread located in the boot. I only use it to show my friends the attention to detail Fiat has put in!

Things I have used.
1) All media player settings through B&M
2) made calls through B&M (voice and by buttons)
3) Follow me home headlamps are tested.
4) Fuel lid opened from the boot(Well just to test it).
5) Anti glare IRVM.
6) Fog lamps I use more often.
8) foldable seats.

Things I have NOT used.
1) 12V socket.
2) B&M message reader.(not compatible with my canvas 4)
3) never tried rear seat belt myself as I am the driver all the time. Although I have made my mother wear it.
4) Trip meter B.
5)Heater. Car has seen only the Summer as she's only few months old.

Never used
1) Rear sun curtains
2) Follow-me head lamps (checked once myself and demonstrated once to my wife, but never got an real life situation to use)
3) Never opened any door / boot with mechanical key